1. Field of the Invention
The present invention relates to a photoelectric conversion module, and more particularly, to a photoelectric conversion module which improves the optical coupling efficiency.
2. Description of the Related Art
In the present information and communication technologies, optical communication technologies are developed to achieve high speed communication environments according to high speed and high capacity data transmission. In the optical communication, a photoelectric conversion device of a sender converts an electric signal into an optical signal, and the converted optical signal is transmitted to a receiver by an optical fiber or an optical waveguide. A photoelectric conversion device of the receiver converts the received optical signal into the electric signal. For the system application and commercialization of these photoelectric conversion devices, the photoelectric conversion devices need to be structured to efficiently achieve the electrical connection and optical coupling.
FIG. 1 is a sectional view illustrating a conventional photoelectric conversion module.
As illustrated in FIG. 1, the conventional photoelectric conversion module comprises: a photoelectric conversion device 10 of a sender and a photoelectric conversion device 20 of a receiver, which are positioned on a printed circuit board (PCB) 30.
The photoelectric conversion device 10 of the sender comprises: a first optical device 12 emitting light to one side of an optical waveguide 32 positioned in the printed circuit board 30, and a first semiconductor chip 14 controlling the first optical device 12. The photoelectric conversion device 20 of a receiver comprises: a second optical device 22 receiving an optical signal transmitted through the optical waveguide 32, and a second semiconductor chip 24 controlling the second optical device 22.
The first and second optical devices 12 and 22 are respectively bonded to lower parts of the first and second semiconductor chips 14 and 24. Further, the first and second optical devices 12 and 22 are respectively positioned to correspond to ends of the optical waveguide 32.
Through connection bumps 16 and 26, the first and second semiconductor chips 14 and 24 are respectively connected to a signal line 34 positioned on the printed circuit board 30, to be electrically connected to the printed circuit board 30.
The driving characteristics of the conventional photoelectric conversion module in the above-described structure will be described below:
The first optical device 12 converts an electric signal into an optical signal, based on the control of the first semiconductor chip 14 of the photoelectric conversion device 10 of the sender. The optical signal converted by the first optical device 12 is reflected through a first micro mirror 32a and is transmitted into the optical waveguide 32. The first micro mirror 32a is positioned at the end of the optical waveguide 32 on the part of the sender. The optical signal transmitted into the optical waveguide 32 is reflected through a second micro mirror 32b and is input into the second optical device 22 of the photoelectric conversion device 20 of the receiver. The second micro mirror 32b is positioned at the end of the optical waveguide 32 on the part of the receiver. The second optical device 22 receives the optical signal transmitted through the optical waveguide 32, converts the optical signal into the electric signal and outputs the electric signal, based on the control of the second semiconductor chip 24.
In the conventional photoelectric conversion module, since the first and second optical devices 12 and 22 are positioned to be spaced apart from each other perpendicularly to the direction in which the optical waveguide 32 extends, the optical coupling efficiency is decreased. In general, a vertical cavity surface emitting laser (VCSEL) is used as the first optical device 12. When the vertical cavity surface emitting laser emits light in the air, its emission angle is about 25˜30 degrees. Therefore, as the distance between the vertical cavity surface emitting laser and the optical waveguide 32 becomes greater, the optical coupling efficiency is considerably decreased.
As a part to solve the problem in that the optical coupling efficiency is decreased, the conventional photoelectric conversion module has presented a scheme to improve the optical coupling efficiency by positioning lenses 36a and 36b between the first and second optical devices 12 and 22 and the optical waveguide 32. Since the lenses 36a and 36b prevent the light emitted from the vertical cavity surface emitting laser from spreading, the optical coupling efficiency could be improved. However, since the number of the lenses 36a and 36b to be positioned is increased according to the distance between the first and second optical devices 12 and 22 and the optical waveguide 32, there are the problems in that an additional process is needed to position the lenses 36a and 36b between the first and second optical devices 12 and 22 and the optical waveguide 32 and this additional process becomes an obstacle in mass production.
Further, in the conventional photoelectric conversion module, the micro mirrors 36a and 36b respectively sloping at specific angles are positioned in the ends of both sides of the optical waveguide 32, to reflect the light emitted from the first optical device 12 so as to be directed into the optical waveguide 32 and to reflect the light transmitted through the optical waveguide 32 so as to be directed to the second optical device 22. However, processes with many steps are required to manufacture the micro mirrors 36a and 36b in a metal thin film having a thickness of about several tens of microns, to position the micro mirrors 36a and 36b so as to slope at specific angles, and to align the micro mirrors 36a and 36b with an optical axis at accurate positions during the process of manufacturing the photoelectric conversion module. Moreover, the reliability of the photoelectric conversion module is greatly decreased during this process.
As described above, in the conventional photoelectric conversion module, since the optical coupling efficiency is decreased by the vertical distance between the optical devices and the optical waveguide, light loss is caused when light is emitted or received. Moreover, since the micro mirrors, lenses and the like are additionally formed or positioned to solve the problem in that the optical coupling efficiency is decreased, the process of manufacturing the photoelectric conversion module becomes complicated. Moreover, since the devices, such as the micro mirrors, are manufactured in a micro-miniature structure, in fact, not only it is difficult to match the devices with the optical axis but also the devices are easily damaged during the manufacturing process. Consequently, both process and production costs increase.